The enthalpies of formation [∆H 0 f (g)] of pentacyclo[4.4.0.0 2,5-.0 3,8 .0 4,7 ]dec-9-ene (9, basketene) and pentacyclo[4.4.0.0 2,4 .0-3,8.0 5,7 ]dec-9-ene (14, snoutene) have been determined by measurement of their heats of combustion in a microcalorimeter as 110.2 ± 0.5 kcal·mol −1 and 78.4 ± 0.3 kcal·mol −1 , respectively. These values and the strain energies (SEs) [SE(9) = 110.3 kcal·mol −1 , SE(14) = 78.4 kcal·mol −1 ] derived from them were compared with values obtained from MM2/ MM3 calculations. The enthalpy of isomerization of 9 to tricyclo[4.2.2.0 2,5 ]deca-3,7,9-triene (8, Nenitzescu's hydrocarbon) was measured by differential scanning calorimetry (DSC) as −20.7 ± 0.3 kcal·mol −1 (384.1 K), corresponding to a strain energy SE(8) of 44.6 kcal·mol −1 . The enthalpy of activation for this rearrangement was also determined from the DSC measurements to be 28.6 ± 0.1 kcal·mol −1 . The obtained strain energies and the derived heats of isomerization to 9,10-dihydronaphthalene (7) did not correlate in any way either with the activation energies of the thermal isomerizations of these Families of (CH) n hydrocarbons are characterized by the multiple rearrangements into one another that their members can undergo. [1] These rearrangements can be initiated [a]
Eine Reihe sekundarer Azoalkane 1, R'R'CH -N = N -CHR'R2, R' = t-C,H,, R' = Aryl (meso-und ~,~-l a -i ) und R2 = cyclo-C6HI I (IJ,I,-~ k), wurde synthetisiert, vorzugsweise durch partielie katalytische Hydrierung von Ketazinen. Die Konfiguration von 1 wurde ermittelt durch photochemische Umwandlung kristalliner Proben von 1 in 6, die bevorzugt unter Retention verlief. Die Kinetik der thermischen Fragmentierung von l a -k und I n (R' = CH,, R' = C6HJ) in Radikale 7 wurde mit DSC verfolgt. Die Aktivierungsdaten wurden durch rechnerische Anpassung theoretischer Kurven an die Mematen ermittelt. -Der Zerfall von 1 mit R', R' = Alkyl wird rnit zunehmender G r o k der Substituenten schneller (,,back strain"); die Fragmentierung von l a -i mit R' = Aryl wird dagegen sterisch behindert, 2.B. k[la 10 ' . Kraftfeldrechnungen erklaren beide Effekte rnit der h d erung dcr Spannungscnthalpie H , im Rcaktionsverlauf [Ds = 2 H , (7) -H, (l)]. Ein Anteil von 0.5-0.6 von D, wird kinetisch wirksam als Beitrag zu AG * (150°C). Die Ursache der sterischen Behinderung [z. B. D, (1 a) = 7.8 kcal/mol], die Spannung in den
115ChemInform Abstract The ketazines (I), prepared according to literature procedures, are converted to the title compounds (II) and (III) by partial hydrogenation, as exemplified in the scheme by the syntheses of (IIa), (IIc) and (IIIa). In some cases, an alternative pathway via dichlorides of type (IV) is feasible, leading to either dl or meso isomers. The configuration of the azoalkanes is established by photolysis of crystalline samples, yielding the dimers (V) with retention of configuration. The same products are formed by thermolysis of (II) in the absence of a radical scavenger. The thermal decomposition of (II) and (III) in 9,10-dihydroanthracene to give radicals of type (VI) is studied extensively using a differential scanning calorimeter (kinetics, determination of activation parameters with the aid of a computer program, calculation of strain enthalpies by the force field method, discussion of the resonance effect on the rate of thermolysis).
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